The present invention relates to pedal assemblies in particular to a pedal for vehicle engines employing electronic throttle control systems, wherein the pedal provides a hysteresis force to simulate a mechanical feel to the pedal during operation by a driver of the vehicle.
Electronic controls and computers are well known in the art of automotive manufacturing. It is not unusual for a late model automobile to have a computer for monitoring and controlling many of its operating systems. Typically an input stage may include data collection by sensors. The collected data is input to a processing stage where an electronic control module interprets the data and calculates appropriate output for delivery to an output stage. Actuators within the output stage convert the appropriate output to a desired physical movement. One such operating system includes the electronic throttle control (ETC). In the ETC system, often referred to as a xe2x80x9cdrive-by-wirexe2x80x9d system, the accelerator pedal is not connected to the throttle body by a cable, as in earlier model vehicles, but rather by an electrical connection between the pedal and a throttle controller, as described by way of example in U.S. Pat. Nos. 5,524,589 and 6,073,610. As described by way of example with reference to U.S. Pat. No. 6,098,971, a potentiometer typically replaces the cable that normally runs to the throttle body and electrical wires send pedal position information to a computer. As a result, the pedal must now have its own springs. However, it is desirable to simulate the mechanical feel of a conventional pedal. With each spring having its own feel and no hysteresis effect as does a cable in a sheath, a spring and mechanical hysteresis device is desirable for operation with the pedal for simulating the mechanical feel. A hysteresis force is a controlled frictional force which simulates the friction created in a conventional pedal as the linkage cable is pushed and pulled through a cable sheath. The hysteresis forces have the beneficial effect to a driver, by way of example, of preventing fatigue, as the force needed to maintain a fixed position of the pedal is less than the force to move the pedal to the fixed position. In addition, the hysteresis force helps enable the vehicle operator to maintain a fixed pedal position over bumpy roads.
A pedal position sensor provides an electrical voltage output responsive to pedal angular position. The pedal position sensor typically includes a resistive potentiometer which replaces the cable that normally runs to the throttle body of the vehicle engine. As described in U.S. Pat. No. 6,098,971 to Stege et al., and as is well known in the industry, problems inherent with drive-by-wire systems include the need for the pedal to have its own spring, and with its own spring, the feel of the pedal can change from pedal to pedal and manufacturer to manufacturer. To provide a desirable feel, pedals used with electronic controls have included hysteresis devices that provide varying friction during depressing and releasing of the pedal. Typically, and as further described in U.S. Pat. No. 6,098,971, a pedal module for use with ETC systems includes return springs operable with hysteresis elements that provide a varying force against the pedal when being operated between an idle position and an accelerating control position, by way of example.
Various measures of hysteresis force are defined in vehicle manufacturer""s specifications for ETC accelerator pedals. In some cases a constant hysteresis force is specified, but in others a hysteresis force which increases with applied pedal force is preferred. Also, the amount of hysteresis force as a percentage of applied force has generally increased as the specifications have become more refined. The need to provide a mechanism which produces a controllable, and xe2x80x9ctuneable,xe2x80x9d hysteresis force of significant magnitude presents a challenge to the pedal designer.
With no hysteresis force the applied pedal force is balanced by the force from the return spring. The hysteresis force is a form of friction force which subtracts from the applied force as the pedal is being depressed and subtracts from the spring force as the pedal is being returned toward its idle position. Such friction force depends on a normal force being generated at a frictional surface. A number of arrangements of springs and friction pads, or washers are known. However, there remains a need for a low cost pedal that is simple to fabricate using plastic molding technology and can be tuned to a broad range of customer requirements.
In view of the foregoing background, it is therefore an object of the present invention to provide a pedal operable with an electronic throttle controller that can be easily and effectively modified to meet varying hysteresis requirements. It is further an object of the present invention to provide a reliable yet inexpensive hysteresis effect for a pedal.
These and other objects, advantages and features of the present invention are provided by a pedal having a base and a pedal beam rotatably connected to the base. An arm member is pivotally coupled to the pedal beam and includes a friction surface that slidably engages a surface of the base for movement on the surface during rotation of the pedal beam. In one preferred embodiment, a compression spring provides means for biasing the pedal beam and arm member toward a preselected position through a biasing force on the arm member, while simultaneously biasing the friction surface of the arm member against the surface of the base, wherein rotating the pedal beam with an applying force to a free end thereof results in a frictional force between the arm member and the base with an increasing displacement of a pedal free end. Further, reducing the displacement through a retracting force returns the pedal to the preselected position through a hysteresis force response for the pedal beam displacement, wherein the retracting force is less than the applying force by a predetermined amount for a preselected displacement.
A method aspect of the invention provides a preselected hysteresis force response during displacement of a pedal. The pedal includes the pedal beam pivotally connected to the base for rotation about a shaft carried by the base. The method includes pivotally coupling an arm member to the pedal beam. The arm member has a friction surface positioned for engaging a surface of the base for slidable movement thereon. The pedal beam is biased toward a preselected position through a biasing force on the arm member, while simultaneously biasing the friction surface of the arm member against the surface of the base. As a result, rotating the pedal beam with an applying force to a free end of the pedal beam creates a frictional force between the arm member and the base with an increasing displacement of a pedal free end. In addition, reducing the displacement through a retracting force returns the pedal to the preselected position through a hysteresis force response for the pedal beam displacement, wherein the retracting force is less than the applying force by a predetermined amount for a preselected displacement.
By providing the arm member with first and second arm portions of a preselected length dimensions, a preselected biasing of the friction surface of the arm member against the surface of the base can be achieved. In addition, with a longitudinal axis of the arm member extending through a pivot point thereof, and with the friction surface engaging the surface of the base along a friction plane axis oriented at a non-zero angle to the longitudinal axis of the arm member, orienting the friction plane axis at a preselected orientation provides an alternate method of providing desired frictional forces and thus a desired hysteresis. Yet another method includes modifying friction surface materials so as to change their coefficients of friction.
A method further includes sensing rotation of the pedal beam for providing an electrical signal representative of pedal rotation about the rotation axis and thus pedal pad displacement.